Today, fabrics are made from a wide-variety of natural fibers, such as cotton, synthetic fibers, and combinations thereof. The basic fabric is a greige fabric that must be dyed or bleached in order to provide the desired whiteness and brightness to the resultant fabric and/or garment. In the case of knitted fabrics, the basic greige fabric is tubular, meaning that both inner and outer surfaces of the tube must be dyed or bleached.
There are numerous known methods for bleaching fabrics, including the use of continuous ranges and high temperature jets. Continuous range bleaching involves a multiple step process, including the application of an optical brightener to make the fabric look whiter following a fabric rinse and nip step. In some cases, this requires re-handling of the fabric, which adds to process time. The fabric must be handled again as it is moved to a pad machine for the application of a softener that improves the hand to the fabric, and then to a dryer. In high temperature jet bleaching, the bleaching chemicals are applied at higher temperatures than are obtained in a continuous range, and optical brighteners are exhausted onto the fabric. In this process, however, the size of the load of fabric in the jet vessel is limited, therefore increasing the time and labor required to load and unload smaller quantities of fabric. The fabric must then be moved to the pad machines for application of a softener. Thereafter, the fabric must be moved to the dryers.
A further disadvantage of conventional bleaching or dyeing, for example, in current jet vessels, is the relatively large amount of water required. In current jet vessels, the liquor ratio may be as high as 10:1. As used herein, the term “liquor ratio” means the quantity in pounds of water per pound of fabric used to perform the initial bleaching process. Thus, each pound of fabric to be bleached or dyed requires about 10 pounds (1.2 gallons) of water. In the conventional process, the bleaching or dyeing step must be followed by 3 to 4 consecutive rinses with water to free the fabric of residual hydrogen peroxide, sodium hydroxide, and other residuals found in cellulosic fabric (seeds, waxes, natural oils, knitting and spinning oils, etc.). In the case of a 10:1 ratio, this would require 30 to 40 pounds of water, or a total of about 50 pounds (6.0 gallons) of water to complete the bleaching and rinsing process for each pound of fabric.
Spray bleaching of fabric is also possible, although a disadvantage of spray bleaching is the lack of uniform bleaching on both sides of the fabric. Achieving such uniformity requires spraying both sides of the fabric or garment in a very controlled environment. Also, the fabric or garment must remain in a taut position in order to provide a flat and even distribution of the bleach formulation onto the fabric or garment, yet not have any area that is covered or unavailable for receipt of the spray.
What is needed, therefore, is a method for bleaching cellulosic, especially greige, fabrics that provide uniform scouring and/or bleaching on both the inner and outer sides of the fabric that minimizes the amount of water and chemicals used. Such a method would allow bleaching cotton to the desired whiteness in one basic spray step or operation and eliminate the need for a controlled environment and the problems noted above for positioning the fabric or garment, yet would provide good bleach penetration into the fabric or garment.
The above-described and other advantages and features of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description and appended claims.